How do I import an advanced auto-generated rig to Unity?
1) Metarig (Rigify, actually) is a good efficient rig, AutoRig Pro is fast and fancy, but it's not very "solid", it has some limitations and some techincal troubles that I personally find quite annoying, and Blenrig is more cartoony squash and stretch oriented.

2) Rigify is the simplest, but you can perform edits on every rig, as soon as you understand their structure

3) Only Auto Rig Pro (out of thoose 3) has a built in retargeting panel, but there are many other ways to retarget an animation on a new rig (addons, manually, ...)

4) the usual workflow is: perform the animation, select in pose mode only deform bones (in Rigify they are all on the 30th Bone Layer), go to Pose_Animation_Bake Action to bake their action into a new action (Only selected, visual keying, remove constraints), and export that action along with a rig composed by deforming bones only (as Fbx works quite well).

Note: Blenrig uses lots of Blender tricks (Lattices, Shape keys, ...) that make it hard to export, if you don't want any headache try to use animations bone made only.

So short answer is: Rigify is the best for your tasks, unless you want to use the Auto Rig Pro retargeting features.

Use T pose as rest pose for best results.